One to three million children in Africa will die of malaria this year. To control malaria, several vaccine approaches are being developed, one of which is against the sexual stages (aka a transmission-blocking vaccine). The genes encoding four potential transmission-blocking target antigens (Pfs25, Pfs28, Pfs40, and Pfs230) of transmission-blocking antibodies have now been cloned in our laboratory, and a fifth, a parasite-produced chitinase, and a sixth, a mosquito-produced protease, have been identified. Of the four target antigens that have been cloned, all have been expressed in one or more recombinant expression systems, but only rPfs25 and rPfs28 have induced transmission-blocking antibodies in laboratory animals. Our immediate goals are to 1) test in humans the safety, immunogenicity, and efficacy of a rPfs25 subunit vaccine and design a means of testing the efficacy of such a transmission-blocking vaccine in the field, 2) improve expression of the rPfs28 that induces blocking antibodies and test various combinations of rPfs25 and rPfs28 in a cocktail vaccine suitable for use in humans to determine if the combination elicits longer lasting or higher titer transmission-blocking antibodies, 3) determine the role, if any, that the calcium-binding Pfs40 plays in sexual development and ascertain if Pfs40 is a target of transmission-blocking antibodies, 4) improve the expression of rPfs230 so that it induces antibodies equivalent to those of transmission- blocking mAbs to Pfs230, 5) isolate and express the genes encoding the parasite-produced chitinase and mosquito-produced proteases, and 6) isolate analogous genes to the five parasite proteins, if they exist, from P. vivax. Our more long-term goals include identifying new target antigens on sexual stage parasites, and defining the molecular mechanisms involved in fertilization of malarial parasites.